Ventrus Biosciences Inc said its lead experimental drug to treat anal fissures failed to reduce pain more than a placebo in a late-stage trial, sending its shares plunging 67 percent in premarket trading. In May 2012, the company had shown the treatment, codenamed VEN 307, was superior to a dummy drug for the same indication, in another late-stage trial. Ventrus said on Wednesday that gastrointestinal disorders were the most common adverse events reported by the 434 patients in the study, which aimed to reduce anal pain associated with or following defecation.